\begin{tikzpicture}
  [node/.style={circle, draw}]
  \matrix 
  [matrix of nodes,
  nodes in empty cells,
  row sep={4em,between origins},
  column sep={2em,between origins}]
  {
    &&\node[node](n4){4};&&\\
    &&\node[node](n3){3};&&\\
    \node[node](n1){1};&&&&\node(n2)[node]{2};\\
  };
  \node[right=of n4,xshift=-2.5em] (n4r) {\bcancel{$t_4$ | $y$}};
  \node[above=of n4r,yshift=-3em] {$y$ | $t_4$};
  \node[left=of n4,xshift=2.5em] {*};
  \node[right=of n3,xshift=-2.5em] (n3r) {\bcancel{$t_3$ | $x$}};
  \node[above=of n3r,yshift=-3em] {$x$ | $t_3$};
  \node[left=of n3,xshift=2.5em] {-};
  \node[right=of n1,xshift=-2.5em] {15 | $t_1$,$a$,$t_2$};
  \node[right=of n2,xshift=-2.5em] {$y$};
  \draw[-] (n4) -- (n3);
  \draw[-] (n3) -- (n1);
  \draw[-] (n3) -- (n2);
  \draw[-] (n4) to [in=90,out=-150] (n1);
\end{tikzpicture}